1. Field of the Invention
This invention relates to the field of optical lithography, and in particular to printing patterns on the following substrates: wafers; printed circuit boards; flat panel displays; masks; reticles; and plates used for the reproduction of magazines, newspapers and books.
2. Description of the Related Art
The semiconductor industry uses very expensive stepper tools for lithographic processing. Furthermore, very expensive reticles are used in this processing—the cost of the reticles is sufficient to make low volume production of chips (such as custom ASICs) prohibitively expensive. The semiconductor industry needs a lower cost lithography process. Furthermore, every time the lithography pattern changes, several days or more are required to produce a new reticle. The semiconductor industry needs a lithography process which can quickly accommodate pattern changes.
The printed circuit board (PCB) industry has similar problems with its lithography processes. Furthermore, the substrates used in the PCB industry undergo distortion during fabrication which limits the use of high resolution lithography processing to small area substrates and the use of steppers. A high resolution lithographic process is required for large PCB substrates in which the pattern can be quickly and economically adjusted to accommodate the distortions, where the distortions vary from one substrate to the next.
U.S. Pat. Nos. 5,330,878 5,523,193 5,482,818 and 5,672,464 to Nelson describe a method and apparatus for patterning a substrate. The apparatus uses a spatial light modulator (SLM), specifically the Texas Instruments deformable mirror device (DMD), in place of a reticle. The DMD is an array of individually controllable reflective elements. An image of the DMD is projected on the substrate by an imaging lens. Whether or not an individual element of the DMD reflects light into the imaging lens, such that it is projected on the substrate, is determined by computer; thus the pattern projected on the substrate is computer controlled and readily changed. Improvements are required to this approach in order to meet the high resolution and throughput requirements of both the semiconductor and PCB industries. Furthermore, advancements are available to reduce the cost of the apparatus, while increasing the throughput and meeting the high resolution requirements.